The present invention relates to electrical conductors and, more particularly, to electrical conductors for transmitting electrical power that are shielded from electromagnetic effects.
Electrical systems aboard aircraft are susceptible to electromagnetic effects (EME). As used herein, EME includes electromagnetic interference (EMI), such as transient voltage and current spikes caused by lightning, as well as electromagnetic compatibility (EMC) issues. Such electrical systems often include long runs of conductors that convey electric current from a source, such as a battery, generator or circuit panel, to a load, such as a motor, a light or other electrical component. For example, a lightning strike may cause electric voltage or current to be induced in the conductors, where it travels to and may damage electrical components.
The effect of a lightning strike may be mitigated somewhat in an aircraft made of a conductive material such as aluminum. A lightning strike may be conducted along the skin of an aircraft made of aluminum and not induce significant electric current in the conductors of on-board electrical systems. However, with the introduction of aircraft made partly or entirely of composite materials, such as carbon fiber composites, the ability of the skin of an aircraft to conduct electricity and therefore act as a shield for internal electrical conductors from external EMI such as lightning strikes, is reduced or eliminated, which may require greater shielding of electrical conductors.
Typically, an electrical conductor, such as that found in a power feeder system, may provide three-phase power. The three-phase power may be created by a generator on board the aircraft and transmitted by cables to a bus or load, such as a three-phase motor. The feeder system in such an application may include three discrete, insulated cables wrapped around a neutral cable, forming a bundle. The bundle of four cables may be enclosed in a sheath of braided metallic material (commonly referred to as a shield) that is grounded at its ends. The braided metallic material may be covered by a sheath of insulating material, and may be separated from the bundle of conductors and neutral cable by a layer of insulated material.
The metallic sheath that covers the entire bundle of conductors and the neutral cable may add to the non-payload weight of the aircraft, which is undesirable. Moreover, by enveloping the entire cable bundle in a grounded, metallic sheath, which in turn may be covered by an insulative sheath, there is a risk of unacceptable heat build-up within the sheath. Accordingly, there is a need for a power feeder system that provides adequate protection from transient voltage spikes resulting from EME, such as lightning strikes to an aircraft, and which minimizes heat build-up and weight.